Amid the increase in demand for a reduction in the Total Cost of Ownership (TCO) of a company information system and for reduced power consumption, over-provisioning of storage has become problematic. The over-provisioning involves the failure of capacity planning prior to the introduction of a system and the mounting of a greater number of disks than the disk capacity which the host computer actually requires. The over-provisioning produces an increase in the TCO due to the wasteful investment in equipment in the information system and causes the wasteful power consumption which is caused by the running of unused disks.
Technology which serves to avoid over-provisioning has in recent years included the installation of thin provisioning in the disk arrays. This is a virtual disk technology which provides a host computer with a virtual disk volume and allocates physical disk space from a pool of backend physical disks in accordance with the writing of data. According to this technology, a plurality of host computers share a single physical disk pool via a virtual disk volume and physical disk space is allocated to the virtual disk volume in accordance with the amount of stored data. As a result, because there is no need to provide each host computer with a capacity margin, the total disk capacity of the whole system is reduced.
However, there remain problems with thin provisioning of a normal disk array from the perspective of the capacity efficiency while the system is running. The disk array does not possess information on the file system of the host computer. Hence, the disk array is unable to know that a file has been erased from the file system of the host computer and that the physical disk space is not being used. After the creation of the file system, the physical disk space allocated to the virtual volume is not collected until the file system has been erased. For this reason, in a system in which the physical disks are exhausted, another file system is unable to utilize an unused physical disk even when a large quantity of files in a certain file system are erased. As a result, the disk utilization efficiency of the whole system is reduced.
As a technology for solving the problem of capacity efficiency with such thin provisioning, the technology that appears in Japanese Application Laid Open No. 2005-11316, for example. According to this technology, the disk array reads a journal log of the file system from a specified disk space (journal disk space) of the corresponding virtual volume, analyzes the content, detects the erasure of files by the file system and specifies the disk space of the erased files, and collects the corresponding physical disk space from the virtual disk volume. That is, the corresponding physical disk space is disk space that can be allocated.
Furthermore, Japanese Application Laid Open No. 2005-11316 also discloses technology that ends the allocation of real disk space which has not been used when the system administrator has issued a defragmentation start instruction.
However, in garbage collection (GC) technology of physical disk space which uses the journal log, it is judged whether the writing of the journal occurs, when the writing of the journal occurs, it is analyzed whether there is real disk space which can be liberated, and real disk space which can be liberated is liberated. Hence, when the erasure and updating of files with respect to a specified file system are a frequent occurrence, the function drops significantly in comparison with a system which does not run a thin provisioning function. This is because the processor managing the corresponding virtual disk volume performs the analysis of the journal log, the allocation of physical disk space, and the liberation of physical disk space, which are required for thin provisioning very frequently, in parallel with the normal data read processing and data write processing. In addition, in a situation where the erasure and the updating of the files are frequent, there is the risk that, following the GC of the storage disk space of the physical disks from a certain disk space of the virtual disk volume, the storage disk space of the physical disk will be immediately allocated to the same disk space, that the allocation of the storage disk space of a physical disk which is not required if not collected must be re-executed and that the processing efficiency relating to the I/O of the system will be wastefully reduced.
In addition, in cases where the allocation of real disk space which has not been used is liberated when the system administrator issues a defragmentation start instruction, there is the risk that GC processing will be executed even when the physical disk space which can be allocated is sufficient and that processing efficiency relating to the I/O of the system will be diminished. There is also the risk that, in cases where files are frequently erased and updated and so forth, as mentioned earlier, the storage disk space of the physical disk which is not required if not collected must then be allocated and the processing efficiency relating to the I/O of the system will be wastefully diminished.